This invention is an improvement on a Modular Digital Image Generator, Ser. No. 394,229 filed July 1, 1982, U.S. Pat. No. 4,930,233) by the present applicant and Judit K. Florence, and assigned to the same Assignee as the present invention. The disclosure in Ser. No. 394,229 therefore, is incorporated by reference herein.
Since the first development of computer-generated image systems to display a view out of the window of a simulator cockpit, efforts have been under way to increase the realism that such images are capable of providing. Efforts have been successful in providing the effective training cues needed to train a pilot. However, the realism viewed in a scene has escaped all efforts up to now.
It has long been felt that having a computer-generated image system with an effective translucency capability would be extremely desirable, particularly for simulation of translucent clouds and smoke as well as for dynamic shadowing effects. More importantly, it can be used for blending two adjacent levels of detail of images to effect gradual level of detail change. This level-of-detail blending capability is useful especially for gradual re-introduction of an image as a pilot moves closer and closer to it and gradual fading of an image as the pilot recedes from it.
Real-time computer-generated image systems, particularly the so-called "out-of-the-window visual systems", have increased greatly the scope of simulator training. With these computer-generated image systems, it is possible to train pilots in visually referenced flight maneuvers such as landing, takeoff, navigation, and weapon delivery.
A typical computer-generated image system as used in the past has been arranged as a "scanline based" processor. This means that an image is generated scanline-by-scanline synchronously as it is displayed.
The basic operation of the "scanline based" processor is found in an article entitled "Computer Image Generation for Flight Simulation" by B. Schachter in Computer Graphics and Applications, dated October, 1981.
Therefore, the scanline based processor used in the past has included a geometric processor, a scanline computer, a video generator, and an appropriate display device. The geometric processor is interfaced with a data base which supplies the geometric processor with the information that is used to process a particular image.
In particular, this information has included a description of the images that are to be displayed. The images are defined by a list of "faces" and the faces, in turn, are defined by a list of "edges".
Translucency capability is utilized also to simulate level-of-detail blending in the following manner. Each image to be displayed is modeled to several levels of detail. Rather than switching from one level to the next as a function of the angular subtense of the image, the switching is done gradually from one level to the next using translucency capability as described in detail hereinafter.
The geometric processor is furnished with a list of faces which describes images to be displayed. The geometric processor will act on this list of faces and perform elimination of backward-facing surfaces, geometric transformations and a process called "windowing".
Furthermore, the geometric processor customarily will provide a tonal description of each face, such as shading and fading. The results of the geometric processor computations are stored in a memory and are transmitted to a scanline computer.
The scanline computer normally uses the information received from the geometric processor to determine which of the faces are occulted and which of the faces are to be displayed on the display device. In particular, the scanline computer works on edge "intersections" and, as its name suggests, processes the edge intersection information serially, one display scanline at a time. Since the displayed image is generated scanline by scanline, this scanline-based computer-generated image system performance is in part limited by its ability to handle the most complex scanline, i.e., is limited by a maximum number of edge intersections per scanline to produce an acceptable displayed image.
The output of the scanline computer usually is connected to a video processor. In such video processor, the information for displaying the visible faces, which is furnished by the scanline computer, is transformed into picture-element-by-picture-element information. As used hereinafter, the term "picture element" is called a "pixel".
To review briefly, the video processor transforms the pixel information into a digital format that corresponds to the intensity of each displayed pixel. Finally, the video processor provides a mechanism so that the digital pixel information is converted into an analog electrical voltage (or a video signal) which is used to drive a display in a raster format.
The display customarily includes a conventional projector or a cathode ray tube. A typical cathode ray tube display has a succession of equidistant scanlines, where each scanline is made up of many picture elements (called pixels). The cathode ray tube constructs a displayed image by interlacing two separate "fields", where one field contains even-numbered scanlines and the other field contains odd-numbered scanlines. The interlaced fields are called a "frame".
Although the particular scanline based processor that has been developed in the past provides an important advance in the art of computer-generated image systems for flight simulation particularly, it does not fully satisfy the objectives of enhancing realism to the point that is appropriate for modern simulator uses. The scanline based processor's arrangements are limited in their ability to handle the more complex scanlines. The limitation is due to the time available to process a scanline while maintaining synchronism with the display.
This and other insufficiencies of the prior art computer-generated image systems suggest that a need has existed for a new approach to a solution to these problems. The present invention provides such a new approach, and it improves upon the ability of prior computer-generated image systems.